This application is a 371 of PCT/EP01/01569 filed on Feb. 13, 2001.
1. Field of the Invention
The present invention relates to a process for the production of industrial tubes or section bars from metal, and relates to an apparatus employed for such production. More particularly, the present invention relates to a process of continuous casting to obtain metal tubes and section bars for industrial use, especially intended for heat exchange, i.e., usable for heat exchangers or desalting plants and in the field of chemical and petrochemical plants.
2. Description of the Related Art
The materials suitable for the production of such metal tubes and section bars include copper and alloys thereof, cupronickel, special brasses, aluminum bronze, and the like.
As is known, these materials have several characteristics that render them suitable for the purpose, such as, for instance, a high electrical and thermal conductivity, a good corrosion resistance, and an excellent hot and cold workability.
In the production of these tubes and section bars, reference is made to specific directives and norms that define the chemical composition and the tolerances of the material; such norms are, for instance, the American Society for Testing and Materials (ASTM) B111 norm; the Deutsches Institut fxc3xcr Normung e.V. (DIN) 1785 norm, with DIN being the German Institute for Standardization which is similar to the American National Standards Institute (ANSI); the Ente Nationale Italiano di Unificazione (UNI) 6785 norm, with UNI being an Italian standards body; and the Association Francaise de Normalisation (AFNOR or NFA) 51.102 norm, with AFNOR and/or NFA being a French standards body.
Such metal tubes and section bars for industrial use are conventionally obtained by means of a process that comprises many operating steps, and that, besides causing the process to be a log, laborious, and not easily realizable one, markedly affects the cost of the finished product.
The known processes, in fact, comprise, starting from the classification of raw materials and scraps, a first step of melting the material in induction electric ovens, with preparatory treatments such as titration and alligation. Afterwards, from the casting molten material, billets are obtained, i.e. half-finished cylindrical products having a diameter generally comprised between 80 mm. and 350 mm. Billets are submitted to cutting and lumping operations, to be then transferred, in right size, on drawing presses, on prior heating to a temperature comprised between 700xc2x0 C. and 1,100xc2x0 C. By means of such presses, preforms are obtained having a tubular shape or other shapes, which are submitted to dimension and quality controls in general, and conveyed afterwards to a rolling mill and/or die to cold-reduce their cross-section.
This working step causes approximately an 80% reduction in the body sections, whose diameter and thickness elongate and reduce. Sometimes, in the presence of particular allows to be worked, intermediate thermal treatments are required, to make the cold working of the preforms easier. Subsequent drawing operations produce the almost finished product, whose cross-section is further reduced. The actual finishing comprises the cutting of the pieces, a possible straightening thereof, as well as controls and examinations, on prior degreasing or cleaning.
This obviously long and laborious process requires the use of many specific materials and generates a high percentage of wastes and scraps in the various steps, both during the melting which causes the realization of the billets, and during hot drawing, and also afterwards. In the general economy of the production cycle, the generation of scraps causes, in the whole, a total yield ratio equal to about 2:1.
Besides, also the costs of the plants, referring to the cast ovens and the drawing presses, are far from being negligible, as they contribute to increasing the production cost of the product.
An object of the present invention is to obviate the above drawbacks.
More particularly, an object of the present invention is to provide a process for the realization of metal tubes or section bars for industrial use to be employed as heat exchangers, desalting plants, or chemical and petrochemical plants, that comprises a limited number of operating steps and assures a finished product provided with all the requirements needed with respect to precision, reliability, and metallographic structure.
A further object of the invention is to provide a process as defined above such as to involve, for its implementation, only limited requirements from the production plants.
A further object of the invention is to provide users with a process for the realization of metal tubes and section bars able to substantially reduce not only the length of the production plant, but also the amount of scraps generated.
According to the present invention, these and still other objects, which will become apparent from the following description, are achieved by a process for the production of tubes or section bars from metal, that comprises the following operating steps:
melting metal with possibly compatible working scraps;
obtaining a preform from the molten metal;
roll milling and/or drawing the preform to reduce the cross-section thereof;
drawing, by means of one or more concatenated interventions, the same preform up to the size desired;
strengthening and possibly submitting to thermal and/or degreasing treatments the dimensionally finished product; and
cutting to measure the finished product.
The preform may have any shape, but the tubular shape is preferred.
The apparatus for the realization of the process, which is also an object of the invention, comprises a crucible and an ingot mold provided with axial and radial holes, communicating with each other, to feed the molten metal coming from the crucible. Preferably, the latter has, in the inside, a central chamber pressurized preferably with inert gases, in order to keep constant the pressure of the zone feeding the ingot mold.